The invention relates generally to graded barrier coatings. More specifically, the invention relates to graded barrier coatings that are used with substrates, devices and the like.
Many devices are susceptible to reactive chemical species, such as oxygen or water vapor, normally encountered in the environment. Such devices are found in certain electrochromic devices, liquid crystal displays, organic light emitting diodes (“OLEDs”), light emitting diodes, photovoltaic devices, radiation detectors, medical diagnostic systems, integrated circuits, sensors, packaging and other components. Reference is made in this specification to non-limiting exemplary OLED embodiments; however, one of ordinary skill in the art will appreciate the applicability of the present invention to other devices and substrates.
EL devices, which may be classified as either organic or inorganic, are known in the graphic display and imaging arts. EL devices have been produced in different shapes for many applications. Inorganic EL devices, however, typically suffer from a required high activation voltage and low brightness. On the other hand, OLEDs, which have been developed more recently, offer the benefits of lower activation voltage and higher brightness in addition to simple manufacture, and, thus, the promise of more widespread application. The meaning of the acronym OLED herein is intended to include all variations of organic electroluminescence devices and their names, including, for example, light emitting polymers (LEP) and organic electroluminescence (OEL) devices.
Most organic electronic devices, especially OLEDs, are prone to rapid degradation when exposed to moisture and oxygen. Conventional OLEDs are built on transparent glass substrates that provide a low transmission rate of oxygen and water vapor. Glass substrates, however, are most suitable for rigid applications. Applicants have found manufacturing processes involving glass substrates to be relatively slow and costly in some circumstances. While plastic substrates provide flexibility, they are not impervious to oxygen and water vapor, and, thus, have provided insufficient protection for OLEDs.
In order to improve the resistance of these substrates to oxygen and water vapor, alternating layers of organic and inorganic compositions, including polymeric and ceramic materials have been applied to a surface of a substrate. In such multilayer barriers, a polymeric layer decouples defects in adjacent ceramic layers to reduce the transmission rates of oxygen and/or water vapor through the channels made possible by the defects in the ceramic layer. The interface between layers, however, may be weak and prone to delaminate.
The alternating layers discussed above commonly have different indices of refraction, normally resulting in degradation in optical transmission through the multiple layers. Prior approaches have focused on engineering the thickness of the layers to improve light transmission efficiency by taking advantage of multiple-interference patterns. One has to retain certain thickness of the layers, however, in order to maintain performance as a barrier. Furthermore, in a mass production environment it is difficult to achieve exact thickness control of the layers. Thus, engineering the thickness to accommodate optical transmission has presented certain challenges.
Current methods use glass or metal can encapsulation or glass or metal substrates, in combination with multi-layer coatings. While these methods may give good barriers, they have limited ability to satisfy the varying requirements for manufacturing of electronic devices, particularly optoelectronic devices, including both passive and active matrix OLEDs, bottom and top emission OLEDs, and both rigid and flexible devices. For example, for optical or optoelectrical devices, the coated barrier may be required to transmit, reflect or absorb light in a predefined manner. The coated barrier may be required to have certain qualities, such as having a certain flexibility, thickness, or durability. The coated barriers may further be required to adapt to different manufacturing needs such as barrier, tact time, OLED compatibility and yield. Traditional barriers have had a limited ability to provide the versatility required.
There remains a need for barriers that, in various embodiments, ameliorate or improve upon one or more of the deficiencies of the prior art.